1. Field of the Invention
The present invention relates to a dielectric film and a method for manufacturing the same, and more particularly, to a dielectric film comprising a thermoplastic resin and finely divided dielectric porcelain particles and a method for manufacturing the same.
2. Brief Description of the Prior Art
A thermoplastic resin formed body with finely divided dielectric porcelain particles dispersed therein is known as a dielectric body which has a high dielectric constant and excellent formability. Such a formed body can be easily prepared in the form of a thin film which has a relatively great dielectric constant and hence a relatively great electrostatic capacitance.
For example, Netherland Pat. No. 7,105,397 discloses unstretched thermoplastic moulding materials comprising thermoplastic resins and barium titanate, and U.S. Pat. No. 4,010,133 describes an unstretched dielectric film comprising an internally plasticized thermosetting resin and dielectric particles dispersed in the crosslinked polymer.
Also, composite films of finely divided porcelain particles and polyvinylidene fluoride which are neither cross-lined nor stretched are disclosed by, for example, T. Yamada et al (Chem. Abstract 97-32074 (1982)) and E. Fukada et al (Chem. Abstract 88-144926 (1978)).
Other materials which may be used for dielectric film but do not contain dielectric porcelain particles are discribed by Mateev, K. V. at al (Chem. Abstract 76-15101 (1972)) who teach crosslinking of polyvinylidene fluoride, and by Wang, T. T. (Chem. Abstract 97-73294 (1982)) who teaches polyvinylidene fluoride films having improved thermal stability associated with the formation of crosslinks in the polymer.
However, with the recent trend toward smaller capacitors for more compact electric equipment, the electrostatic capacitance obtainable with the materials as described above is not yet satisfactory. A dielectric film which has greater electrostatic capacitance is desired.
One method of achieving this is to make a formed body into a thinner film. However, in a formed body of a composite system containing a thermoplastic resin and finely divided dielectric porcelain particles, stretching results in a reduced dielectric constant.